FIG. 5 is a sectional view of a conventional micro pump of the sort mentioned above, wherein reference numeral 1 denotes a cylindrical pump body. A head member 2 having a suction port 2a and a discharge port 2b is fixedly fitted into one end of the pump body 1, nozzles being connected to the respective ports 2a, 2b. An external threaded screw 3b at the lower end of a magnetostrictive material 3 (i.e., the lower end on the page face and may be turned to any direction when the pump is operated) is screwed into the internal thread la of the body 1 in order to accommodate the magnetostrictive material 3. A coil 4 is wound on the intermediate portion 3a of the magnetostrictive material 3, which incorporates an upper large-diameter portion 3c for use as a piston and is also fitted with sealing rings 17 in the respective outer peripheral grooves 3d of the large-diameter portion 3c, so that a chamber 5 is formed in between the magnetostrictive material 3 and the head member 2.
The head member 2 includes a valve seat 2e, a ball 6, a spring 7 for urging the valve element 6 to the valve seat 2e, and a spring shoe 8, these being provided in an inlet flow channel 2c communicating with the suction port 2a. The head member 2 also includes in the opposite direction a valve seat 2f, a ball 9, a spring 10 and a spring shoe 11, these being provided in an outlet flow channel 2d.
In the pump as mentioned above, there is produced an alternating magnetic field each time a driving power supply 12 energizes and deenergizes the coil 4 alternately and repeatedly. As a result, the magnetostrictive material 3 elongates and contracts, whereby the large-diameter portion 3c, which acts as a piston, ascends and descends to enlarge or reduce the space of the chamber 5. In the discharge condition, the valve element 9 of the outlet valve ascends to open and the valve element 6 of the inlet valve also ascends to close. On the other hand, in the suction condition, the valve element 9 of the outlet valve descends to close and the valve element 6 of the inlet valve also descends to open. The liquid discharge and suction conditions are alternately repeated so as to cause the liquid sucked from the suction port 2a to flow into the chamber 5 and to flow out of the discharge port 2b.
By providing a permanent magnet for applying a bias magnetic field to the magnetostrictive material, the magnetic field produced in the coil becomes smaller and the size of the coil can be made small-sized. Therefore, a greater discharge quantity is readily obtainable.
However, the springs 7, 10 that are intended for use in such a conventional micro pump and offer delicate spring force as well as excellent durability are not of standard available size. Even though it is attempted to make the pump operate to suck and discharge a liquid in a steady state with the presence of air in the chamber 5 when it is started at a frequency in the range of, for example, 50 Hz.about.60 Hz, that is, by means of a commercial power supply, self-priming .xi.to suck the liquid into the chamber 5 single-handedly is infeasible because the springs 7, 10 are too stiff. In other words, the chamber 5 will have to be filled with a liquid beforehand and the problem is that such work is troublesome.
In order to solve the foregoing problem, it is proposed a micro pump so constructed that springs can be dispensed with as shown in a sectional view of FIG. 6A. In FIG. 6A, reference numeral 13 denotes a housing with an internal thread 13a which is screwed to an external thread 1a at the lower end of a cylindrical pump body 1. A bobbin 14 with a coil 4 wound thereon is abut against the housing 13 to accommodate the bobbin in the cylindrical pump body 1. A magnetostrictive material 3 is disposed into the bobbin 14 and also made to abut against the housing 13 using a positioning yoke 15.
Reference numeral 16 denotes a first spring shoe which abuts against the upper end of the magnetostrictive material 3. The first spring shoe 16 has an outer peripheral groove 16a to fit a buffering ring 42 made of rubber or plastic so as to make the ring 42 abut against the inner peripheral face of the body 1. Moreover, the spring shoe 16 has a boss 16b projecting on its central surface externally on which bellivile springs 18, a flat washer 20 and a second spring shoe 21 are movably mounted. Reference numeral 22 denotes a piston which is fixed by screwing an external thread 22a into an internal thread 16c provided in the center of the boss 16b of the first spring shoe 16 and has a cylindrical vertical wall 22b on its outer periphery.
Reference numeral 23 denotes a valve-fitting end plate which has an outer peripheral groove 23a to fit a sealing ring 43 made of rubber or plastic so as to make the sealing ring 43 abut against the inner peripheral face of the vertical wall 22b of the piston 22. Further, a cylindrical spacer 24 is provided between the second spring shoe 21 and the flange 23b of the end plate 23. Reference numeral 25 denotes a housing on the head side, in which an internal thread 25b is screwed with an external thread 1b at the upper end of the pump body 1. In this condition, the flange 23b of the end plate 23 is pressed by the flange 25a of the housing 25 against the spring force of the bellivile springs 18. These members are accommodated in such a state. Further, a chamber 26 is formed between the end plate 23 and the piston 22.
Reference numerals 27, 39 denote an inlet valve and an outlet valve fitted to the end plate 23, respectively. The inlet valve 27 is fitted by screwing the external thread at the leading end of a nozzle 27a into the threaded hole 23c of the end plate 23 and a valve body 28 is screwed to the nozzle 27a. A nozzle joint 29 is also screwed to the valve body 28. As shown in an enlarged view of FIG. 6B, in the valve body 28, there are provided a valve seat 44, a ball 6 and a spacer 30 for regulating the gap between the ball 6 and the valve seat 44 by setting the depth of a retainer 32 to constitute a check valve.
More specifically, the retainer 32 is fitted by screwing an external thread on the outer periphery of the retainer 32 into the internal thread 28c of the valve body 28. The retainer 32 is equipped with a gap-adjusting screw 31 which is vertically movable, so that the gap h between the ball 6 and the valve seat 44 is made adjustable by vertically moving the screw 31.
The outlet valve 39 is fitted by screwing the head of the external thread into the threaded hole 23d of the end plate 23. Further, in a valve body 34, there are provided a valve seat 45, a ball 9, a spacer 36 and a retainer 38 having a screw 37 in the direction opposite to what is followed in the inlet valve 27 to constitute a check valve. The gap between the ball 9 and the valve seat 45 is made adjustable likewise. A nozzle joint 35 is also screwed to the outlet valve 39.
When the coil 4 in the aforementioned micro pump is energized, the magnetostrictive material 3 elongates against the spring force of the bellivile spring 18 and the piston 22 moves upward, thus causing the chamber 26 to contract. As the magnetostrictive material 3 contracts when the coil 4 is subsequently deenergized, the piston 22 is lowered by the spring force of the bellivile spring 18 using the first spring shoe 16 and the chamber 26 expands. As the chamber 26 expands or contracts, the balls 6 and 9 inside the valves move vertically, that is, the liquid discharge condition resulting from the ascension of the balls 6, 9 and the liquid suction condition resulting from the descent of the balls 6, 9 are alternately repeated. The pump can thus prime itself and start transferring liquid.
When driver using conventional AC voltage the pump of FIG. 6 (same as pump of FIG. 5 without valve springs) attains a low self-priming height because of the great inertia force of the balls 6 and 9 as shown in a characteristic drawing of FIG. 7 when it is attempted to increase a flow rate by widening the gap h. Consequently, there has arisen the problem of rendering it infeasible to devise a micro pump whose self-priming level is high enough for practical use and which offers a high flow rate.